Radiometer Testbed Development for SWOT

Conventional altimeters include nadir looking colocated 18-37 GHz microwave radiometer to measure wet tropospheric path delay. These have reduced accuracy in coastal zone (within ~50 km from land) and do not provide wet path delay over land. The addition of high frequency channels to Jason-class radiometer will improve retrievals in coastal regions and enable retrievals over land. High-frequency window channels, 90, 130 and 166 GHz are optimum for improving performance in coastal region and channels on 183 GHz water vapor line are ideal for over-land retrievals. We have developed MMIC LNAs that had more than 50% lower noise temperature (NT=300K) than previous state-of-art. The MMIC LNAs enabled us to develop internally calibrated direct detect radiometer testbeds at the required observation frequencies. Our current 166 GHz radiometer testbed system has a noise temperature of 455 K, bandwidth of 10% and operates with 60 mW of DC power. Index Terms — microwave radiometry, humidity measurement, monolithic millimeter wave integrated low noise amplifier, internally calibrated radiometer.